364 CEUSTACEA 



579, 4) and have a variety of functions, being locomotory and respiratory 

 and often serving for the attachment of the eggs or the young. The 

 appendages are all primarily biramose except the anterior antennae, 

 although in the adult animal either the exopodite or the endopodite may 

 be absent and the appendages thus become uniramose. The eyes are either 

 pedunculate or not. The subclass contains 3 divisions and over 11,200 

 species. 



Key to the divisions of Malacostraca: 



! Abdomen composed of 8 segments; large carapace present. .1. PHYLLOCARTDA 



o 2 Abdomen of 7 segments or less. 



&! Carapace absent ; thorax usually with 7 free segments 2. ARTHROSTBACA 



6 a Carapace present covering a part or all of the thorax ... 3. THORACOSTRACA 



DIVISION 1. PHYIiLOCARIDA.* 



Primitive Malacostraca with a thorax bearing 8 pairs of leaf-like 

 gills, a long abdomen composed of 8 segments bearing 6 pairs of 

 appendages and with a large carapace enclosing the head, thorax, 

 and a portion of the abdomen ; eyes pedunculate : 2 genera and 7 

 species, all marine. 



NEBALIA Leach. Caudal 

 fork (furca) with lateral spines: 

 4 species. 



N. bipes (Fabricius) (Fig. 

 574). Body slender, compressed, 

 10 mm. long; genital opening on 

 the last thoracic segment in the ^ 574 _y rtflBfl Wpe . (Packard), 



male and on the antepenultimate 



segment in the female; eggs carried by the female between the thoracic 

 feet: North Atlantic, in shallow water, among seaweeds; Europe. 



DIVISION 2. ARTHROSTRACA. 



Malacostracans of small but not minute size in which the first 

 thoracic somite (in a few cases the second also) is united with the head, 

 the remaining 7 being free and appearing as distinct segments; no 

 carapace present; abdominal somites more or less coalesced, 6 free seg- 

 ments usually appearing, although the number is very often smaller; 

 appendages well developed, consisting, when all are present, of 2 pairs 

 of antennae, 1 pair of mandibles, 2 pairs of maxillae, 1 pair of maxilli- 

 peds (belonging to the first thoracic segment which is fused with the 

 head), 7 pairs of periopods and 6 of pleopods; eyes in most cases ses- 



* See "The Order Phyllocarida," etc., by A. S. Packard, Twelfth Ann. Rep. U. S. 

 Geol. Sur. for year 1878, pt. 1, 1883, p. 432. "The Crustacean Nebalia," by A. S. 

 Packard, Am. Nat., Vol. 16, p. 861. 



